Chemical process for the production of an acid salt of hydroxylamine



Patented Feb. 17, 1953 UNITED (STATES. PATENT OFFICE CHEMICAL PROCESSFOR THE PRODUCTION OF AN ACID SALT OF HYDROXYLAMINE Richard Edward Benson, Clay'mont, DeL, assignor' to E. I. du Pont' de Nemours &' Company,

Wilmington, Del., a corporation of Delaware No Drawing. Application November 8, 1950,

Serial No. 194,735 7 3 Clai'ms'. 1 This invention relates to a new process for preparing hydroxylamine.

Hydroxylamine has longbeen regarded as a potentially important chemical intermediate in a' wide variety of organic and inor anic syntheses. However, despite its versatility in preparing a varied group of useful compounds, this material has not been exploited appreciably in the field of industrial chemistry due toits high cost, which is in turn traceable to the lack ofa cheap, commercial synthesis for this material. Even now, despite the vast advances made in chemical technology, this compound is available commercially from only one supplier and at prices so high (approximately $1.20 to $1.85 per pound) as to prohibit its use in all but a fewapplications. f

Several methods have been uncovered in the past for the preparation of hydrox'ylamine, for instance, through the electrolysis of nitrates, through the acid hydrolysis of primary nitroparafilns, and through hydrolysis of the sul'.

fonate prepared by theoreaction between sodium bisulfite, sodium nitrite and sulfur dioxide under slightly alkaline conditions. However, for various reasons, such as low yields, poor conversions, costly raw materials, and. high operating and equipment costs, these methods cannot be used to produce low-cost hydroxylamine inappreciable concentrations.

Several investigators, notably Butterworth and Partington, Trans. Faraday Soc., 26, 144 (1930); Jouve, Compt. rend. 128, 435 (1899); and Cooke, Proc. Phil. Soc., Glasgow, 18, 291 (1887); have demonstrated the fact that hydroxylamine can be prepared directly by the catalytic hydrogenation of nitric oxide. However, despite thefact that the raw materials required are cheap, the various methods reported by these investigators do not represent successful commercial syntheses since only very low conversions and yields (about 2-3%) are obtained. Thus', it1wou1d= be necessary to concentrate the reaction mixtur'es produced quite thoroughly, e. g., a reductionv in volume of. the orderof 15 to 25 fold, before the product could be obtained in useful concentrations. Such a procedure has not proven: possible' due tothe high rate of thermal. decomposition of free hydroxylamine. Furthermore; even if methods were worked out to successfully accomplish such a concentration, the high operamake it impossible to produce low-cost hydroxyle amine.

In the applicant's copending application S. N.

11 2,841,filed August 2'7, 1949, it ispointed out that platinum in strong acidic solution (i. e.,.

pH less than 2.50 and preferably less than 2.25) serves as a. surprisingly efficient heterogeneous catalyst for the hydrogenation of nitric oxide to hydroxylamin'e, provided that the mole ratio of nitric oxide to hydrogen is less than 1, prefer-.

ably in the range 0.87 (1:15) to 0.167 (1':6.0) the hydroxylamine being. obtained as the salt of the strong acid used. It has been found that other of the noble metals, particularly those of The remaining metals of grou VIII, i. e.,the

members'ofthe firsttriad, iron, cobalt,- and nickel, are, of course, completely inoperative as heterogeneous catalysts for this hydrogenation,

since under the conditions used, the metals readily dissolve in the reaction medium and thus obviate any possibility of heterogeneous catalysis.

It is an objectof the present invention to provide a more economical and commercially practical method of preparing hydroxylamine. A further objectis toprovide a method of pre paringhydroxylamine which requires only simple equipment, yet produces a gOod yield. An

tional costs due to the volume of solutions and solvents necessarily handled'and the equipment restrictions necessarily" involved in avoiding appreciable decomposition of the product would additional object is to provide a method of pre-' paring hydroxylamine from low cost, readily available materials. Other objects will appear from thefollowing detailed description of the invention.

In direct contradiction to the prior art ings: noted, I have found that the foregoing objects are attained by the hydrogenation, at

temperatures ranging from the various freezing points of the reaction mixture to 86 0., of nitri oxide in the presence of a" palladium catalyst andastrong mineral acid, the molarratio of nitric oxide to hydrogen being less than 1. For the" highest yields and best" conversions, it is'p'referred to carry out the hydrogenation reac-v tion at temperatures in the range of 0 C; to

The following examples in which theparts given are by weight unless otherwise indicated are submitted to further illustrate and not to limit this invention:

Example I A glass reactor, fitted with an air-cooled condenser, a sealed stirrer, a thermometer, and a fritted glass gas inlet tube connected through a suitable mixing vessel to sources of gaseous hydrogen and nitric oxide and so arranged that the input of both gases can be separately measured, is charged with 376 parts of a aqueous hydrochloric acid solution and 1 part of 10% palladium-on-charcoal catalyst. Hydrogen is passed into the reaction mixture at 150-250 parts by volume per minute at 40-45 C. for 10 minutes, and the reaction vessel then cooled to 31 C. The input hydrogen rate is then adjusted to 159 parts by volume per minute and nitric oxide admitted to the reaction zone at a rate of 39 parts by volume'per minute over a period of one hour at 3l-33 C. with vigorous stirring. The reaction is continued for an additional two hours at a temperature ranging from -31 C. with nitric oxide and hydrogen being admitted to the reaction zone at rates, respectively of 37-40 and 158-160 parts by volume per minute; The reaction mixture is then cooled to 2 to 3 C. and the reaction continued for an additional three hours at this temperature with nitric oxide and hydrogen being admitted to the reaction zone at rates, respectively, of 39-40 and 150-154 parts by every hour andanalyzed for nitric oxide content.

In this manner the per cent of nitric oxide reacted is obtained; These results are summarized to require 21.8 parts by volume of a 0.1069 N potassium permanganate solution to oxidize back to the ferric ion stage. This corresponds to a total of 1.79 parts of hydroxylamine in the re-- action mixture which, based on the nitric oxide combined using the above given average nitric oxide conversion of 53%, represents 17.9% of the theoretical yield of hydroxylamine, obtained as the hydrochloride. Another sample of the reaction mixture analyzed similarly yields identical results.

Example II Another reaction is carried out utilizing the same equipment and operating procedure as described in Example I but varying in that nitric oxide and hydrogen are admitted tothe reaction zone at rates, respectively, of 49-53 and 102-115 parts by volume per minute. In this instance, there is obtained a 6.7% yield of hydroxylamine as the hydrochloride at an average nitric oxide conversion of 18%.

Example III Another reaction is carried out again utilizing the same equipment and operating procedure except that in this case the initial temperature range is 28-29 C., and the gaseous nitric oxide and hydrogen are admitted to the reaction zone at rates, respectively, of 35-38 and 122-128 parts by volume per minute. From this reaction, there is obtained'a 14% yield of hydroxylamine again obtained as the hydrochloride at an average nitric oxide conversion of 45%.

Example IV Another reaction is carried out in the same equipment and manner as previously described except that the reaction temperature is increased from 31 C. to 79 C. over a period of 5 hours with nitric oxide and hydrogen being admitted to the reaction zone at rates, respectively, of 40-42 and 166-169 parts by volume per minute. In this reaction, 13.7% of the nitric oxide introduced into the reaction vessel is converted to hydroxylamineagain as the hydrochloride.

The importance of pH in this reaction has already been mentioned. At values of pH appreciably greater than 7, only relatively small quantities of hydroxylamine can be prepared by inthe following table: this reaction procedure. Best results in this syn- Parts of Reaction Parts of Oil Gas Avg. Per- Avg. Per- Time, 96 N0 by Parts by cent NO cent NO Hours 1 VOL/Min. X -VQL Mm. 041 Gas) Reacted 33 39 159 172 10. 1 55. 2 31 40 150 155 9. 2 51. 7 31 37 158 159 5.5 75.5 5 39 150 184 12.4 41.5 2 39 154 181 12.9 40.0 V 2 I 40 c 153 183 12.5 42.3,

thesis are obtained by operating at a pH below 2, e. g., in the range from 0.01 to 2.

The acids which have been used successfully are the common, strong, inorganic, i. e., mineral acids, e. g., hydrochloric, nitric, sulfuric, and

' 'drogen being used in the reaction mixture.

a solution containing an excess of ferric ions produces a solution containing sufiicient ferrous ions 1:2 or slightly lower are still operable. In the phosphoric acids.

.As has been mentioned previously, it is important that a careful control be maintained of the relative proportions of nitric oxide and hy- For best results it is necessary that nitric oxide to hydrogen ratios less than one and preferably from 1:3 to 1:6 be used, although ratios as low as most preferred range of 1:3 to 1:4 maximum yields and conversion are obtained in the preferred pH and temperature ranges irres ective of other operating conditions, provided that the peratures from 5.--to' 30 C., are preferred. Re-

action conditions similar to those given in Example I are those preferred in continuous operations, although operation under superatmospheric pressure is also possibly carried out in a continuous fashion; g

The efiiciency and success of this reaction are nowise dependent ,;on operating pressures. The reaction is equall'yjg efiicient, in the preferred ranges of temperaturanpH and nitric oxide to hydrogen ratios, at atmospheric pressuresa's well as at 1,000 lb./sq:;i n.' pressures or higher. From the standpoint of simplicity of equipmentyit is preferable to operate in the range of from 1 to 50 lb'./sq. in. In this connection, it should be mentioned that in those reactions involving the'jhandling of nitric oxide/hydrogen gas mixtures under pressures appreciably above atmospheric,;for example, over 50 lbI/sq. in., especially in thelrelative proportions previously mentioned as preferred in the process of this inventiongi ei itreme care should be taken since it is known that these mixtures are potentially explosive.

Although only palladium-on-charcoalfcatalysts are mentioned in the examples, palladium catalysts of various types known in the art can be used, for instance, metallic palladium itself, palladium-on-kieselguhr, or palladium on "any one of the known acid-resistant catalyst carriers, palladinized or not. i Hydroxylamine is well known to the chemical art as a valuable intermediate in the preparation of a number of chemical compounds. Hydroxylamine prepared by the process of this invention can be used in many reactions described in the literature for this compound. As pointed out previously, the process of this invention leads to,

the direct preparation of the hydroxylamine acid salt with whatever acid is being used. If free hydroxylamine is desired, it can be readily chtained from the hydroxylamine acid salt by direct neutralization with a strong base such as, sodium hydroxide. Because of the greater stability and resistance to degradation of the hydroxylamine acid salts, and the correspondingly greater ease in using them, they are commercially the normal form in which hydroxylamine is used. Q1

While the invention has been described in detail in the foregoing, it will be appreciated that the examples given are illustrative only and that many variations may be made by "the skilled chemists without departure from the scope of the present invention. Accordingly, I intend to be limited only by the following claims.

I claim:

1. A process for the catalytic hydrogenation of nitric oxide to produce an acid salt of hydroxylamine which comprisescatalytically hydrogenating nitric oxide with elemental hydrogen in a medium consisting essentially of water, a palladium catalyst and a strong mineral acid, said v medium having a pH of less than and being maintained at a temperature between the freezing point of the reaction mixtureand C., the molar ratio of the nitric oxide ,.to the elemental hydrogen present being less than 1.

2. A process as claimed in claim 1;wherein the molar ratio of nitric oxide to hydrogen is in the range from 1:2 to 1:6.

3. A process as claimed in claim 1 wherein the temperature is maintained between 0 C. and 30 C.

RICHARD EDWARD BENSON.

REFERENCES CITED The following references are of record in the file of this patent: 

1. A PROCESS FOR THE CATALYTIC HYDROGENATION OF NITRIC OXIDE TO PRODUCE AN ACID SALT OF HYDROXYLAMINE WHICH COMPRISES CATALYTICALLY HYDROGENATING NITRIC OXIDE WITH ELEMENTAL HYDROGEN IN A MEDIUM CONSISTING ESSENNTIALLY OF WATER, A PALLADIUM CATALYST AND A STRONG MINERAL ACID, SAID MEDIUM HAVING A PH OF LESS THAN 2 AND BEING MAINTAINED AT A TEMPERATURE BETWEEN THE FREEZING POINT OF THE REACTION MIXTURE AND 80* C., THE MOLAR RATIO OF THE NITRIC OXIDE TO THE ELEMETAL HYDROGEN PRESENT BEING LESS THAN
 1. 